Kamikaze Wasp Technique: could irradiation-induced sterility in parasitoids provide a feasible option for the contribution of biological control to insect pest eradication?

Abstract

The Sterile Insect Technique (SIT) is an effective and environmentally friendly eradication tool. Its combination with biological control can be synergistic, which could improve an SIT-based eradication programme. However, stringent regulations requiring risk assessments prior to approvals to release classical biological control (CBC) agents limits their use as a component of eradication. Applying the SIT to parasitoid CBC agents could eliminate non-target risk and potentially provide a pathway for the contribution of biological control to eradication by alleviating conventional risk assessment processes. I have termed this novel concept the Kamikaze Wasp Technique (KWT). Irradiation exposure permanently inhibited offspring emergence from Trissolcus basalis (Hymenoptera: Scelionidae) females. If these were to be released, they would not form a self-sustaining population, eliminating the irreversible risk of non-target impacts. There was no difference in the time spent searching and arrested on host-contaminated arenas between sterile and non-sterile T. basalis females. In large laboratory cages, there was also no difference in the ability of sterile females to locate and parasitise Nezara viridula (Hemiptera: Pentatomidae) egg masses. Host-searching ability is therefore retained in sterile T. basalis, which bears implications for cost-effectiveness. By irradiating different age cohorts of T. basalis females, I observed that older parasitoids incurred a higher degree of sterility. Parasitoids irradiated at the oldest age also exhibited longer searching times on host-contaminated arenas, suggesting that host-searching behaviours are more sensitive to irradiation damage in younger T. basalis. Age at the time of irradiation can therefore influence the biosafety and efficacy of the KWT. Finally, I modelled the efficacy of combined releases of sterile male pentatomids and sterile female parasitoids. The integration of sterile parasitoids and SIT outperformed the SIT used alone. In laboratory cages, the combination of sterile male N. viridula and sterile T. basalis induced higher F1 egg mortality than the SIT used alone. Sterile parasitoids could improve the chances of success of SIT-based eradication programmes. This study demonstrates the feasibility of a new tool that could improve the efficacy of environmentally friendly eradication. To expand the proof-of-concept into potential application, large scale field studies must be conducted to demonstrate real-word efficacy.